dictyNews Electronic Edition Volume 39, number 8 March 15, 2013 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= Phase geometries of two-dimensional excitable waves govern self-organized morphodynamics of amoeboid cells. Daisuke Taniguchią ,Shuji Ishiharaą , Takehiko Oonuki, Mai Honda-Kitahara, Kunihiko Kaneko, and Satoshi Sawai (ą equal contribution) 1. Graduate School of Arts and Sciences, and 2. Research Center for Complex Systems Biology, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan; 3. Precursory Research for Embryonic Science and Technology (PRESTO), JST, Kawaguchi, Saitama 332-0012, Japan PNAS, in press In both randomly moving Dictyostelium and mammalian cells, phosphatidylinositol (3,4,5)-trisphosphate and F-actin are known to propagate as waves at the membrane and act to push out the protruding edge. To date, however, the relationship between the wave geometry and the patterns of amoeboid shape change remains elusive. Here, by using phase map analysis, we show that morphology dynamics of randomly moving Dictyostelium discoideum cells can be characterized by the number, topology, and position of spatial phase singularities, i.e., points that represent organizing centers of rotating waves. A single isolated singularity near the cellular edge induced a rotational protrusion, whereas a pair of singularities supported a symmetric extension. These singularities appeared by strong phase resetting due to de novo nucleation at the back of preexisting waves. Analysis of a theoretical model indicated excitability of the system that is governed by positive feedback from phosphatidylinositol (3,4,5)-trisphosphate to PI3-kinase activation, and we showed experimentally that this requires F-actin. Furthermore, by incorporating membrane deformation into the model, we demonstrated that geometries of competing waves explain most of the observed semiperiodic changes in amoeboid morphology. Submitted by Satoshi Sawai [cssawai@mail.ecc.u-tokyo.ac.jp] --------------------------------------------------------------------------- The Dictyostelium prestalk inducer DIF-1 directs phosphorylation of a bZIP transcription factor Yoko Yamada, Yuzuru Kubohara1, Haruhisa Kikuchi2, Yoshiteru Oshima2, Hong Yu Wang, Susan Ross and Jeffrey G. Williams* College of Life Sciences, Welcome Trust Biocentre,University of Dundee, Dow St., Dundee, DD1 5EH, UK 1 Department of Molecular and Cellular Biology, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi 371-8512, Japan 2 Laboratory of Natural Product Chemistry, Tohoku University Graduate School of Pharmaceutical Sciences, Aoba-yama, Aoba-ku, Sendai 980-8578, Japan Int J Dev Biol, in press Background DIF-1, a chlorinated hexaphenone produced by developing Dictyostelium cells, induces prestalk differentiation. DimB is a bZIP transcription factor that accumulates in the nucleus upon exposure to DIF-1, where it directly activates transcription of DIF-responsive genes. The signaling steps upstream of DimB and downstream of DIF-1 are entirely unknown. Results Analysis by mass spectrometry shows that incubation with DIF-1 rapidly stimulates phosphorylation at several sites in DimB. We characterize the most highly responsive site, S590, which is located very close to the C terminus. A point mutation in this site, S590A, does not inhibit DimB nuclear accumulation in response to DIF. However, this seems likely to reflect functional redundancy with other sites; because a panel of chemical variants on the structure of DIF-1 show a correlation between their potencies as inducers of DimB nuclear accumulation and their potencies as inducers of phosphorylation at S590. Furthermore the S590A mutant is fully active in mutant rescue of a dimB null strain, arguing against an alternative role in transcriptional activation of target genes. Conclusions i) DIF-1 directs phosphorylation at S590 ii) although it is not essential for nuclear accumulation in response to DIF-1 correlative evidence, based upon a panel of DIF-1 related molecules, suggests that this modification may play a redundant role in the process iii) We also present evidence that the kinase activity, which phosphorylates S590, is non-nuclear and that this signalling pathway is, in part at least, independent of the DIF-regulated STATc activation pathway. Submitted by Jeff Williams [j.g.williams@dundee.ac.uk] ============================================================== [End dictyNews, volume 39, number 8]